1. Field of the Invention
The present invention relates to a treatment, and more specifically to a treatment for treating an organotin compound in a liquid.
2. Description of the Related Art
An organotin compound, in particular, a tributyltin (TBT) compound or a triphenyltin (TPT) compound is useful as a molluscan eliminating agent component for an antifouling paint employed in fishnets or ships, a pesticide for pears or onions, a mouse repellant or an insecticide for wood products and the like, an industrial disinfectant for papermaking or leather processing, etc., and is conventionally used worldwide. In recent years, it has been revealed that the organotin compound has an endocrine disturbing action, and the organotin compound is recognized as a toxic substance providing adverse effects on human health and ecosystem. For example, “Report (proposal) regarding test results of endocrine disturbing action of tributyltin (TBT) to fish” (Environmental Health Department, Environmental Policy Bureau, Ministry of the Environment (August 2001)) and “Present status and temporal trends on imposex and organotin concentrations in tissue of the rock shell, Thais clavigera” (Japan Society of Endocrine Disrupters Research, Abstracts for The 4th Annual Meeting of JSEDR, p. 288 (2001)) each report that snails such as rock shells (Thais clavigera) living at harbors have developed imposex frequently. The imposex refers to a symptom featured in sex change of female snails, and is known to be developed by an effect of a tributyltin compound in an extremely low concentration of about 2 ng/l in seawater.
Thus, in Japan, pesticide registration of the tributyltin compound expired in 1977, and use of the tributyltin compound in household products has been prohibited since 1979. In 1989, tributyltin oxide was designated as a Class I Specified Chemical Substance under “Law Concerning the Evaluation of Chemical Substances and Regulation of Their Manufacture, etc. (Japanese Chemical Substances Control Law)”, and its production, import, and use have been essentially prohibited. In 1990, tributyltin chloride was designated as a Class II Specified Chemical Substance under the same law, and its use and the like has been subjected to regulation. Thus, in Japan, the organotin compound is substantially not used in applications of antifouling paints for fishnets and ships.
However, environmental pollution studies in Japan have confirmed that a pollution level of dredged soil from harbor or seawater from shelf sea or harbor due to the organotin oxide still remains the same, and no significant improvements have been confirmed. Such results have been obtained probably because the organotin compound is hardly decomposed, and foreign ships still use antifouling paints containing organotin compounds. Thus, establishment of techniques for treating dredged soil or seawater polluted with an organotin oxide is desired.
As a method of treating dredged soil in view of the above, a method of decomposing or adsorbing an organotin compound in dredged soil has been known. As an example of the method of decomposing an organotin compound, “Degradation of the tributyltin compounds by the micro-organisms in the water and sediment collected from the harbor area of Osaka City, Japan” (Environmental Pollution 98(2), 163-167, 1997) proposes a method of decomposing an organotin compound by using microorganisms. As another example of the method of decomposing an organotin compound, JP 2001-352994 A proposes a method of decomposing an organotin compound by using active components produced by microorganisms. However, those methods each require a long period of time for decomposition of the organotin compound and each require separation of the microorganisms or extraction of the active components. Thus, those methods tend to be expensive and are probably not practical.
Meanwhile, as an example of the method of adsorbing an organotin compound, JP 2004-160355 A discloses a method involving: adding a flocculant to dredged soil to separate the dredged soil into a solid content (sand and flock settled deposit) and a water content; and adhering and adsorbing the organotin compound in the separated water content to a polyethylene sheet and active carbon, respectively. However, this method has many processing steps and involves complex operations. Further, this method requires use of an expensive polyethylene sheet and a process cost is hardly suppressed.
As examples of a method of treating water such as seawater in view of the above: JP 61-107989 A proposes a method of bringing water into contact with a polyamide substance to allow an organotin compound in water to be absorbed into the polyamide substance; and JP 2005-502457 A proposes a method of irradiating water supplied with ozone with UV light. However, those methods each require an expensive polyamide substance or a complex treatment apparatus, and a process cost is hardly suppressed.